Conductive PTFE bend actuator vented ink jet printing mechanism

Abstract

An inkjet printer having an energy efficient nozzle actuator design which also can be simply constructed. A thermal actuator is activated to eject ink from the nozzle chamber. The thermal actuator includes two layers of actuator material, such as polytetrafluoroethylene, having a high coefficient of thermal expansion, a top layer being substantially non conductive and a bottom layer being conductive, the thermal actuator being activated by means of passing a current through the bottom layer so as to cause it to expand relative to the top. The bottom layer includes portions being conductive and portions being non-conductive such that a resistive circuit is formed. PTFE can be made conductive by the addition of carbon nanotubes. The resistive circuit is created having predetermined areas of low circuit cross-sectional area so as to produce high levels of heating of the actuators in those areas. The actuator has a hydrophobic surface and during operation the hydrophobic surface causes an air bubble to form under the thermal actuator. The bottom surface of the actuator can be further air vented so as to reduce the actuation energy required to eject ink from the nozzle chamber, the venting being by a series of small holes underneath the actuator the holes being interconnected to an air supply channel for supplying air to the back of the actuator.

Description

CROSS REFERENCES TO RELATED APPLICATIONS

The following Australian provisional patent applications are hereby incorporated by cross-reference. For the purposes of location and identification, U.S. patent applications identified by their US patent application serial numbers (USSN) are listed alongside the Australian applications from which the U.S. patent applications claim the right of priority.

CROSS-REFERENCED U.S. PATENT/PATENT AUSTRALIAN APPLICATION PROVISIONAL (CLAIMING RIGHT OF PATENT PRIORITY FROM AUSTRALIAN DOCKET APPLICATION NO. PROVISIONAL APPLICATION) NO. PO7991 09/113,060 ART01 PO8505 09/113,070 ART02 PO7988 09/113,073 ART03 PO9395 09/112,748 ART04 PO8017 09/112,747 ART06 PO8014 09/112,776 ART07 PO8025 09/112,750 ART08 PO8032 09/112,746 ART09 PO7999 09/112,743 ART10 PO7998 09/112,742 ART11 PO8031 09/112,741 ART12 PO8030 09/112,740 ART13 PO7997 09/112,739 ART15 PO7979 09/113,053 ART16 PO8015 09/112,738 ART17 PO7978 09/113,067 ART18 PO7982 09/113,063 ART19 PO7989 09/113,069 ART20 PO8019 09/112,744 ART21 PO7980 09/113,058 ART22 PO8018 09/112,777 ART24 PO7938 09/113,224 ART25 PO8016 09/112,804 ART26 PO8024 09/112,805 ART27 PO7940 09/113,072 ART28 PO7939 09/112,785 ART29 PO8501 09/112,797 ART30 PO8500 09/112,796 ART31 PO7987 09/113,071 ART32 PO8022 09/112,824 ART33 PO8497 09/113,090 ART34 PO8020 09/112,823 ART38 PO8023 09/113,222 ART39 PO8504 09/112,786 ART42 PO8000 09/113,051 ART43 PO7977 09/112,782 ART44 PO7934 09/113,056 ART45 PO7990 09/113,059 ART46 PO8499 09/113,091 ART47 PO8502 09/112,753 ART48 PO7981 09/113,055 ART50 PO7986 09/113,057 ART51 PO7983 09/113,054 ART52 PO8026 09/112,752 ART53 PO8027 09/112,759 ART54 PO8028 09/112,757 ART56 PO9394 09/112,758 ART57 PO9396 09/113,107 ART58 PO9397 09/112,829 ART59 PO9398 09/112,792 ART60 PO9399  6,106,147 ART61 PO9400 09/112,790 ART62 PO9401 09/112,789 ART63 PO9402 09/112,788 ART64 PO9403 09/112,795 ART65 PO9405 09/112,749 ART66 PP0959 09/112,784 ART68 PP1397 09/112,783 ART69 PP2370 09/112,781 DOT01 PP2371 09/113,052 DOT02 PO8003 09/112,834 Fluid01 PO8005 09/113,103 Fluid02 PO9404 09/113,101 Fluid03 PO8066 09/112,751 IJ01 PO8072 09/112,787 IJ02 PO8040 09/112,802 IJ03 PO8071 09/112,803 IJ04 PO8047 09/113,097 IJ05 PO8035 09/113,099 IJ06 PO8044 09/113,084 IJ07 PO8063 09/113,066 IJ08 PO8057 09/112,778 IJ09 PO8056 09/112,779 IJ10 PO8069 09/113,077 IJ11 PO8049 09/113,061 IJ12 PO8036 09/112,818 IJ13 PO8048 09/112,816 IJ14 PO8070 09/112,772 IJ15 PO8067 09/112,819 IJ16 PO8001 09/112,815 IJ17 PO8038 09/113,096 IJ18 PO8033 09/113,068 IJ19 PO8002 09/113,095 IJ20 PO8068 09/112,808 IJ21 PO8062 09/112,809 IJ22 PO8034 09/112,780 IJ23 PO8039 09/113,083 IJ24 PO8041 09/113,121 IJ25 PO8004 09/113,122 IJ26 PO8037 09/112,793 IJ27 PO8043 09/112,794 IJ28 PO8042 09/113,128 IJ29 PO8064 09/113,127 IJ30 PO9389 09/112,756 IJ31 PO9391 09/112,755 IJ32 PP0888 09/112,754 IJ33 PP0891 09/112,811 IJ34 PP0890 09/112,812 IJ35 PP0873 09/112,813 IJ36 PP0993 09/112,814 IJ37 PP0890 09/112,764 IJ38 PP1398 09/112,765 IJ39 PP2592 09/112,767 IJ40 PP2593 09/112,768 IJ41 PP3991 09/112,807 IJ42 PP3987 09/112,806 IJ43 PP3985 09/112,820 IJ44 PP3983 09/112,821 IJ45 PO7935 09/112,822 IJM01 PO7936 09/112,825 IJM02 PO7937 09/112,826 IJM03 PO8061 09/112,827 IJM04 PO8054 09/112,828 IJM05 PO8065  6,071,750 IJM06 PO8055 09/113,108 IJM07 PO8053 09/113,109 IJM08 PO8078 09/113,123 IJM09 PO7933 09/113,114 IJM10 PO7950 09/113,115 IJM11 PO7949 09/113,129 IJM12 PO8060 09/113,124 IJM13 PO8059 09/113,125 IJM14 PO8073 09/113,126 IJM15 PO8076 09/113,119 IJM16 PO8075 09/113,120 IJM17 PO8079 09/113,221 IJM18 PO8050 09/113,116 IJM19 PO8052 09/113,118 IJM20 PO7948 09/113,117 IJM21 PO7951 09/113,113 IJM22 PO8074 09/113,130 IJM23 PO7941 09/113,110 IJM24 PO8077 09/113,112 IJM25 PO8058 09/113,087 IJM26 PO8051 09/113,074 IJM27 PO8045  6,111,754 IJM28 PO7952 09/113,088 IJM29 PO8046 09/112,771 IJM30 PO9390 09/112,769 IJM31 PO9392 09/112,770 IJM32 PP0889 09/112,798 IJM35 PP0887 09/112,801 IJM36 PP0882 09/112,800 IJM37 PP0874 09/112,799 IJM38 PP1396 09/113,098 IJM39 PP3989 09/112,833 IJM40 PP2591 09/112,832 IJM41 PP3990 09/112,831 IJM42 PP3986 09/112,830 IJM43 PP3984 09/112,836 IJM44 PP3982 09/112,835 IJM45 PP0895 09/113,102 IR01 PP0870 09/113,106 IR02 PP0869 09/113,105 IR04 PP0887 09/113,104 IR05 PP0885 09/112,810 IR06 PP0884 09/112,766 IR10 PP0886 09/113,085 IR12 PP0871 09/113,086 IR13 PP0876 09/113,094 IR14 PP0877 09/112,760 IR16 PP0878 09/112,773 IR17 PP0879 09/112,774 IR18 PP0883 09/112,775 IR19 PP0880  6,152,619 IR20 PP0881 09/113,092 IR21 PO8006  6,087,638 MEMS02 PO8007 09/113,093 MEMS03 PO8008 09/113,062 MEMS04 PO8010  6,041,600 MEMS05 PO8011 09/113,082 MEMS06 PO7947  6,067,797 MEMS07 PO7944 09/113,080 MEMS09 PO7946  6,044,646 MEMS10 PO9393 09/113,065 MEMS11 PP0875 09/113,078 MEMS12 PP0894 09/113,075 MEMS13

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

FIELD OF THE INVENTION

The present invention relates to ink jet printing and in particular discloses a conductive PTFE bend activator vented ink jet printer.

The present invention further relates to the field of drop on demand ink jet printing.

BACKGROUND OF THE INVENTION

Many different types of printing have been invented, a large number of which are presently in use. The known forms of print have a variety of methods for marking the print media with a relevant marking media. Commonly used forms of printing include offset printing, laser printing and copying devices, dot matrix type impact printers, thermal paper printers, film recorders, thermal wax printers, dye sublimation printers and ink jet printers both of the drop on demand and continuous flow type. Each type of printer has its own advantages and problems when considering cost, speed, quality, reliability, simplicity of construction and operation etc.

In recent years, the field of ink jet printing, wherein each individual pixel of ink is derived from one or more ink nozzles has become increasingly popular primarily due to its inexpensive and versatile nature.

Many different techniques on ink jet printing have been invented. For a survey of the field, reference is made to an article by J Moore, “Non-Impact Printing: Introduction and Historical Perspective”, Output Hard Copy Devices, Editors R Dubeck and S Sherr, pages 207-220 (1988).

Ink Jet printers themselves come in many different types. The utilisation of a continuous stream ink in ink jet printing appears to date back to at least 1929 wherein U.S. Pat. No. 1,941,001 by Hansell discloses a simple form of continuous stream electro-static ink jet printing.

U.S. Pat. No. 3,596,275 by Sweet also discloses a process of a continuous ink jet printing including the step wherein the ink jet stream is modulated by a high frequency electro-static field so as to cause drop separation. This technique is still utilized by several manufacturers including Elmjet and Scitex (see also U.S. Pat. No. 3,373,437 by Sweet et al)

Piezoelectric ink jet printers are also one form of commonly utilized ink jet printing device. Piezoelectric systems are disclosed by Kyser et. al. in U.S. Pat. No. 3,946,398 (1970) which utilizes a diaphragm mode of operation, by Zolten in U.S. Pat. No. 3,683,212 (1970) which discloses a squeeze mode of operation of a piezoelectric crystal, Stemme in U.S. Pat. No. 3,747,120 (1972) discloses a bend mode of piezoelectric operation, Howkins in U.S. Pat. No. 4,459,601 discloses a piezoelectric push mode actuation of the ink jet stream and Fischbeck in U.S. Pat. No. 4,584,590 which discloses a shear mode type of piezoelectric transducer element.

Recently, thermal ink jet printing has become an extremely popular form of ink jet printing. The ink jet printing techniques include those disclosed by Endo et al in GB 2007162 (1979) and Vaught et al in U.S. Pat. No. 4,490,728. Both the aforementioned references disclosed ink jet printing techniques rely upon the activation of an electrothermal actuator which results in the creation of a bubble in a constricted space, such as a nozzle, which thereby causes the ejection of ink from an aperture connected to the confined space onto a relevant print media. Printing devices utilizing the electro-thermal actuator are manufactured by manufacturers such as Canon and Hewlett Packard.

As can be seen from the foregoing, many different types of printing technologies are available. Ideally, a printing technology should have a number of desirable attributes. These include inexpensive construction and operation, high speed operation, safe and continuous long term operation etc. Each technology may have its own advantages and disadvantages in the areas of cost, speed, quality, reliability, power usage, simplicity of construction operation, durability and consumables.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an alternative form of inkjet printer having an energy efficient nozzle actuator design which also can be simply constructed.

In accordance with a first aspect of the present invention, there is provided an ink jet nozzle comprising a nozzle chamber having an ink ejection port in one wall of the chamber, an ink supply source interconnected to the nozzle chamber and a thermal actuator activated to eject ink from the nozzle chamber via the ink ejection port, the thermal actuator comprising two layers of actuator material having a high coefficient of thermal expansion, a top layer being substantially non conductive and a bottom layer being conductive, the thermal actuator being activated by means of passing a current through the bottom layer so as to cause it to expand relative to the top layer, which is cooled by the chamber ink. Further, the bottom layer comprises portions being conductive and portions being non-conductive such that a circuit is formed for the heating of the bottom layer through the interaction of the conductive and non-conductive portions. Preferably, the resistive circuit is created having predetermined area of low circuit cross-sectional area so as to produce high levels of heating of the actuators in those areas. Advantageously, the non-conductive portions are formed from the same material as the top layer.

In accordance with a second aspect of the present invention, there is provided an ink jet nozzle comprising a nozzle chamber having an ink ejection port in one wall of the chamber, an ink supply source interconnected to the nozzle chamber and a thermal actuator activated to eject ink from the nozzle chamber via the ink ejection port, the thermal actuator being activated by means of passing a current through the bottom layer so as to cause it to expand relative to the top layer. Further, the bottom of the actuator can have a hydrophobic surface and during operation the hydrophobic surface causes an air bubble to form under the thermal actuator. The bottom surface of the actuator can be air vented so as to reduce the actuation energy required to eject ink from the nozzle chamber. Advantageously, the air venting comprises a series of small holes underneath the actuator, the holes being interconnected to an air supply channel for the supply of air to the back of the actuator. Further, the area around the bottom surface of the actuator can be constructed from hydrophobic material. The holes are of a size such that, during operation, any fluid is retained within the nozzle chamber. Preferably, the actuator is attached at one end to the nozzle chamber and the holes are located near the attached end and the actuator is constructed from polytetrafluoroethylene. Further, the actuator can have a bottom layer treated in portions so as to form a conductive material.

BRIEF DESCRIPTION OF THE DRAWINGS

Notwithstanding any other forms which may fall within the scope of the present invention, preferred forms of the invention will now be described, by way of example only, with reference to the accompanying drawings which:

FIG. 1 is a cut out topside view illustrating two adjoining inject nozzles constructed in accordance with the preferred embodiment;

FIG. 2 is an exploded perspective view illustrating the construction of a single inject nozzle in accordance with the preferred embodiment;

FIG. 3 is a sectional view through the nozzles of FIG. 1;

FIG. 4 is a sectional view through the line IV-IV′ of FIG. 3;

FIG. 5 provides a legend of the materials indicated in FIG. 6 to 19; and

FIG. 6 to FIG. 19 illustrate sectional views of the manufacturing steps in one form of construction of an ink jet printhead nozzle.

DESCRIPTION OF PREFERRED AND OTHER EMBODIMENTS

In the preferred embodiment, an inkjet nozzle is provided having a thermally based actuator which is highly energy efficient. The thermal actuator is located within a chamber filled with ink and relies upon the thermal expansion of materials when an electric current is being passed through them to activate the actuator thereby causing the ejection of ink out of a nozzle provided in the nozzle chamber.

Turning to the figures, in FIG. 1, there are illustrated two adjoining inkjet nozzles 1 constructed in accordance with the preferred embodiment, with FIG. 2 showing an exploded perspective and FIG. 4 showing various sectional views. Each nozzle 1, can be constructed as part of an array of nozzles on a silicon wafer device and can be constructed utilising semiconductor processing techniques in addition to micro machining and micro fabrication process technology (MEMS) and a full familiarity with these technologies is hereinafter assumed.

A nozzle chamber 10 includes a ink ejection port 11 for the ejection of ink from within the nozzle chamber. Ink is supplied via an inlet port 12 which has a grill structure fabricated from a series of posts 14, the grill acting to filter out foreign bodies within the ink supply and also to provide stability to the nozzle chamber structure. Inside the nozzle chamber is constructed a thermal actuator device 16 which is interconnected to an electric circuit (not shown) which, when thermally actuated, acts as a paddle bending upwards so as to cause the ejection of ink from each ink ejection port 11. A series of etchant holes e.g. 18 are also provided in the top of nozzle chamber 10, the holes 18 being provided for manufacturing purposes only so to allow a sacrificial etchant to easily etch away the internal portions of nozzle chamber 10. The etchant ports 18 are of a sufficiently small diameter so that the resulting surface tension holds the ink within chamber 10 such that no ink leaks out via ports 18.

The thermal actuator 16 is composed primarily of polytetrafluoroethylene (PTFE) which is a generally hydrophobic material. The top layer of the actuator 16 is treated or coated so as to make it hydrophilic and thereby attract water/ink via inlet port 12. Suitable treatments include plasma exposure in an ammonia atmosphere. The bottom surface remains hydrophobic and repels the water from the underneath surface of the actuator 16. Underneath the actuator 16 is provided a further surface 19 also composed of a hydrophobic material such as PTFE. The surface 19 has a series of holes 20 in it which allow for the flow of air into the nozzle chamber 10. The diameter of the nozzle holes 20 again being of such a size so as to restrict the flow of fluid out of the nozzle chamber via surface tension interactions out of the nozzle chamber.

The surface 19 is separated from a lower level 23 by means of a series of spaced apart posts e.g. 22 which can be constructed when constructing the layer 19 utilising an appropriate mask. The nozzle chamber 10, but for grill inlet port 12, is walled on its sides by silicon nitride walls e.g. 25,26. An air inlet port is formed between adjacent nozzle chambers such that air is free to flow between the walls 25,28. Hence, air is able to flow down channel 29 and along channel 30 and through holes e.g. 20 in accordance with any fluctuating pressure influences.

The air flow acts to reduce the vacuum on the back surface of actuator 16 during operation. As a result, less energy is required for the movement of the actuator 16. In operation, the actuator 16 is thermally actuated so as to move upwards and cause ink ejection. As a result, air flows in along channels 29,30 and through the holes e.g. 20 into the bottom area of actuator 16. Upon deactivation of the actuator 16, the actuator lowers with a corresponding airflow out of port 20 along channel 30 and out of channel 29. Any fluid within nozzle chamber 10 is firstly repelled by the hydrophobic nature of the bottom side of the surface of actuator 16 in addition to the top of the surface 19 which is again hydrophobic. As noted previously the limited size holes e.g. 20 further stop the fluid from passing the holes 20 as a result of surface tension characteristics.

A further preferable feature of nozzle chamber 10 is the utilisation of the nitride posts 14 to also clamp one end of the surfaces 16 and 19 firmly to bottom surface 20 thereby reducing the likelihood delaminating during operation.

In FIG. 2, there is illustrated an exploded perspective view of a single nozzle 1. The exploded perspective view illustrates the form of construction of each layer of a simple nozzle 1. The nozzle arrangement can be constructed on a base silicon wafer 34 having a top glass layer which includes the various drive and control circuitry and which, for example, can comprise a two level metal CMOS layer with the various interconnects (not shown). On top of the layer 35 is first laid out a nitride passivation layer 23 of approximately one micron thickness which includes a number of vias (not shown) for the interconnection of the subsequent layers to the CMOS layer 35. The nitride layer is provided primarily to protect lower layers from corrosion or etching, especially where sacrificial etchants are utilized. Next, a one micron PTFE layer 19 is constructed having the aforementioned holes e.g. 20 and posts 22. The structure of the PTFE layer 19 can be formed by first laying down a sacrificial glass layer (not shown) onto which the PTFE layer 19 is deposited. The PTFE layer 19 includes various features, for example, a lower ridge portion 38 in addition to a hole 39 which acts as a via for the subsequent material layers.

The actuator proper is formed from two PTFE layers 40,41. The lower PTFE layer 40 is made conductive. The PTFE layer 40 can be made conductive utilising a number of different techniques including:

(i) Doping the PTFE layer with another material so as to make it conductive.

(ii) Embedding within the PTFE layer a series of quantum wires constructed from such a material as carbon nano-tubes created in a mesh form. (“Individual single-wall carbon nano-tubes as quantum wires” by Tans et al Nature, Volume 386, Apr. 3rd 1997 at pages 474-477). The PTFE layer 40 includes certain cut out portions e.g. 43 so that a complete circuit is formed around the PTFE actuator 40. The cut out portions can be optimised so as to regulate the resistive heating of the layer 40 by means of providing constricted portions so as to thereby increase the heat generated in various “hot spots” as required. A space is provided between the PTFE layer 19 and the PTFE layer 40 through the utilisation of an intermediate sacrificial glass layer (not shown).

On top of the PTFE layer 40 is deposited a second PTFE layer 41 which can be a standard non conductive PTFE layer and can include filling in those areas in the lower PTFE layer e.g. 43 which are not conductive. The top of the PTFE layer is further treated or coated to make it hydrophilic.

Next, a nitride layer can be deposited to form the nozzle chamber proper. The nitride layer can be formed by first laying down a sacrificial glass layer and etching the glass layer to form walls e.g. 25, 26 and grilled portion e.g. 14. Preferably, the mask utilised results a first anchor portion 45 which mates with the hole 39 in layer 19 so as to fix the layer 19 to the nitride layer 23. Additionally, the bottom surface of the grill 14 meets with a corresponding step 47 in the PTFE layer 41 so as to clamp the end portion of the PTFE layers 41,40 and 39 to the wafer surface so as to guard against delamination. Next, a top nitride layer 50 can be formed having a number of holes e.g. 18 and nozzle hole 11 around which a rim can be etched through etching of the nitride layer 50. Subsequently, the various sacrificial layers can be etched away so as to release the structure of the thermal actuator.

Obviously, large arrays of inkjet nozzles 10 can be created side by side on a single wafer. The ink can be supplied via ink channels etched through the wafer utilising a high density low pressure plasma etching system such as that supplied by Surface Technology Systems of the United Kingdom.

The foregoing describes only one embodiment of the invention and many variations of the embodiment will be obvious for a person skilled in the art of semi conductor, micro mechanical fabrication. Certainly, various other materials can be utilised in the construction of the various layers.

One form of detailed manufacturing process which can be used to fabricate monolithic ink jet printheads operating in accordance with the principles taught by the present embodiment can proceed utilizing the following steps:

1. Using a double sided polished wafer, complete drive transistors, data distribution, and timing circuits using a 0.5 micron, one poly, 2 metal CMOS process. Relevant features of the wafer at this step are shown in FIG. 6. For clarity, these diagrams may not be to scale, and may not represent a cross section though any single plane of the nozzle. FIG. 5 is a key to representations of various materials in these manufacturing diagrams, and those of other cross referenced ink jet configurations.

2. Deposit 1 micron of low stress nitride. This acts as a barrier to prevent ink diffusion through the silicon dioxide of the chip surface.

3. Deposit 2 microns of sacrificial material (e.g. polyimide).

4. Etch the sacrificial layer using Mask 1. This mask defines the PTFE venting layer support pillars and anchor point. This step is shown in FIG. 7.

5. Deposit 2 microns of PTFE.

6. Etch the PTFE using Mask 2. This mask defines the edges of the PTFE venting layer, and the holes in this layer. This step is shown in FIG. 8.

7. Deposit 3 micron of sacrificial material (e.g. polyimide).

8. Etch the sacrificial layer and CMOS passivation layer using Mask 3. This mask defines the actuator contacts. This step is shown in FIG. 9.

9. Deposit 1 micron of conductive PTFE. Conductive PTFE can be formed by doping the PTFE with a conductive material, such as extremely fine metal or graphitic filaments, or fine metal particles, and so forth. The PIFE should be doped so that the resistance of the PTFE conductive heater is sufficiently low so that the correct amount of power is dissipated by the heater when the drive voltage is applied. However, the conductive material should be a small percentage of the PTFE volume, so that the coefficient of thermal expansion is not significantly reduced. Carbon nanotubes can provide significant conductivity at low concentrations. This step is shown in FIG. 10.

10. Etch the conductive PTFE using Mask 4. This mask defines the actuator conductive regions. This step is shown in FIG. 11.

11. Deposit 1 micron of PTFE.

12. Etch the PTFE down to the sacrificial layer using Mask 5. This mask defines the actuator paddle. This step is shown in FIG. 12.

13. Wafer probe. All electrical connections are complete at this point, and the chips are not yet separated.

14. Plasma process the PTFE to make the top and side surfaces of the paddle hydrophilic. This allows the nozzle chamber to fill by capillarity.

15. Deposit 10 microns of sacrificial material.

16. Etch the sacrificial material down to nitride using Mask 6. This mask defines the nozzle chamber and inlet filter. This step is shown in FIG. 13.

17. Deposit 3 microns of PECVD glass. This step is shown in FIG. 14.

18. Etch to a depth of 1 micron using Mask 7. This mask defines the nozzle rim. This step is shown in FIG. 15.

19. Etch down to the sacrificial layer using Mask 8. This mask defines the nozzle and the sacrificial etch access holes. This step is shown in FIG. 16.

20. Back-etch completely through the silicon wafer (with, for example, an ASE Advanced Silicon Etcher from Surface Technology Systems) using Mask 9. This mask defines the ink inlets which are etched through the wafer. The wafer is also diced by this etch. This step is shown in FIG. 17.

21. Back-etch the CMOS oxide layers and subsequently deposited nitride layers through to the sacrificial layer using the back-etched silicon as a mask.

22. Etch the sacrificial material. The nozzle chambers are cleared, the actuators freed, and the chips are separated by this etch. This step is shown in FIG. 18.

23. Mount the printheads in their packaging, which may be a molded plastic former incorporating ink channels which supply the appropriate color ink to the ink inlets at the back of the wafer.

24. Connect the printheads to their interconnect systems. For a low profile connection with minimum disruption of airflow, TAB may be used. Wire bonding may also be used if the printer is to be operated with sufficient clearance to the paper.

25. Hydrophobize the front surface of the printheads.

26. Fill the completed printheads with ink and test them. A filled nozzle is shown in FIG. 19.

It would be appreciated by a person skilled in the art that numerous variations and/or modifications may be made to the present invention as shown in the specific embodiment without departing from the spirit or scope of the invention as broadly described. The present embodiment is, therefore, to be considered in all respects to be illustrative and not restrictive.

The presently disclosed ink jet printing technology is potentially suited to a wide range of printing systems including: color and monochrome office printers, short run digital printers, high speed digital printers, offset press supplemental printers, low cost scanning printers, high speed pagewidth printers, notebook computers with inbuilt pagewidth printers, portable color and monochrome printers, color and monochrome copiers, color and monochrome facsimile machines, combined printer, facsimile and copying machines, label printers, large format plotters, photograph copiers, printers for digital photographic ‘minilabs’, video printers, PHOTO CD (PHOTO CD is a registered trademark of the Eastman Kodak Company) printers, portable printers for PDAs, wallpaper printers, indoor sign printers, billboard printers, fabric printers, camera printers and fault tolerant commercial printer arrays.

Ink Jet Technologies

The embodiments of the invention use an ink jet printer type device. Of course many different devices could be used. However presently popular ink jet printing technologies are unlikely to be suitable.

The most significant problem with thermal ink jet is power consumption. This is approximately 100 times that required for high speed, and stems from the energy-inefficient means of drop ejection. This involves the rapid boiling of water to produce a vapor bubble which expels the ink. Water has a very high heat capacity, and must be superheated in thermal ink jet applications. This leads to an efficiency of around 0.02%, from electricity input to drop momentum (and increased surface area) out.

The most significant problem with piezoelectric ink jet is size and cost. Piezoelectric crystals have a very small deflection at reasonable drive voltages, and therefore require a large area for each nozzle. Also, each piezoelectric actuator must be connected to its drive circuit on a separate substrate. This is not a significant problem at the current limit of around 300 nozzles per printhead, but is a major impediment to the fabrication of pagewidth printheads with 19,200 nozzles.

Ideally, the ink jet technologies used meet the stringent requirements of in-camera digital color printing and other high quality, high speed, low cost printing applications. To meet the requirements of digital photography, new ink jet technologies have been created. The target features include:

low power (less than 10 Watts)

high resolution capability (1,600 dpi or more)

photographic quality output

low manufacturing cost

small size (pagewidth times minimum cross section)

high speed (<2 seconds per page).

All of these features can be met or exceeded by the ink jet systems described below with differing levels of difficulty. Forty-five different ink jet technologies have been developed by the Assignee to give a wide range of choices for high volume manufacture. These technologies form part of separate applications assigned to the present Assignee as set out in the table under the heading Cross References to Related Applications.

The ink jet designs shown here are suitable for a wide range of digital printing systems, from battery powered one-time use digital cameras, through to desktop and network printers, and through to commercial printing systems.

For ease of manufacture using standard process equipment, the printhead is designed to be a monolithic 0.5 micron CMOS chip with MEMS post processing. For color photographic applications, the printhead is 100 mm long, with a width which depends upon the ink jet type. The smallest printhead designed is IJ38, which is 0.35 mm wide, giving a chip area of 35 square mm. The printheads each contain 19,200 nozzles plus data and control circuitry.

Ink is supplied to the back of the printhead by injection molded plastic ink channels. The molding requires 50 micron features, which can be created using a lithographically micromachined insert in a standard injection molding tool. Ink flows through holes etched through the wafer to the nozzle chambers fabricated on the front surface of the wafer. The printhead is connected to the camera circuitry by tape automated bonding.

Tables of Drop-on-Demand Ink Jets

Eleven important characteristics of the fundamental operation of individual ink jet nozzles have been identified. These characteristics are largely orthogonal, and so can be elucidated as an eleven dimensional matrix. Most of the eleven axes of this matrix include entries developed by the present assignee.

The following tables form the axes of an eleven dimensional table of ink jet types.

Actuator mechanism (18 types)

Basic operation mode (7 types)

Auxiliary mechanism (8 types)

Actuator amplification or modification method (17 types)

Actuator motion (19 types)

Nozzle refill method (4 types)

Method of restricting back-flow through inlet (10 types)

Nozzle clearing method (9 types)

Nozzle plate construction (9 types)

Drop ejection direction (5 types)

Ink type (7 types)

The complete eleven dimensional table represented by these axes contains 36.9 billion possible configurations of ink jet nozzle. While not all of the possible combinations result in a viable ink jet technology, many million configurations are viable. It is clearly impractical to elucidate all of the possible configurations. Instead, certain ink jet types have been investigated in detail. These are designated IJ01 to IJ45 which match the docket numbers in the table under the heading Cross References to Related Applications.

Other ink jet configurations can readily be derived from these forty-five examples by substituting alternative configurations along one or more of the 11 axes. Most of the IJ01 to IJ45 examples can be made into ink jet printheads with characteristics superior to any currently available ink jet technology.

Where there are prior art examples known to the inventor, one or more of these examples are listed in the examples column of the tables below. The IJ01 to IJ45 series are also listed in the examples column. In some cases, a printer may be listed more than once in a table, where it shares characteristics with more than one entry.

Suitable applications for the ink jet technologies include: Home printers, Office network printers, Short run digital printers, Commercial print systems, Fabric printers, Pocket printers, Internet WWW printers, Video printers, Medical imaging, Wide format printers, Notebook PC printers, Fax machines, Industrial printing systems, Photocopiers, Photographic minilabs etc.

The information associated with the aforementioned 11 dimensional matrix are set out in the following tables.

ACTUATOR MECHANISM (APPLIED ONLY TO SELECTED INK DROPS) Description Advantages Disadvantages Examples Thermal An electrothermal Large force High power Canon Bubblejet bubble heater heats the ink to generated Ink carrier 1979 Endo et al GB above boiling point, Simple limited to water patent 2,007,162 transferring significant construction Low efficiency Xerox heater-in- heat to the aqueous No moving parts High pit 1990 Hawkins et ink. A bubble Fast operation temperatures al U.S. Pat. No. 4,899,181 nucleates and quickly Small chip area required Hewlett-Packard forms, expelling the required for actuator High mechanical TIJ 1982 Vaught et ink. stress al U.S. Pat. No. 4,490,728 The efficiency of the Unusual process is low, with materials required typically less than Large drive 0.05% of the electrical transistors energy being Cavitation causes transformed into actuator failure kinetic energy of the Kogation reduces drop. bubble formation Large print heads are difficult to fabricate Piezo- A piezoelectric crystal Low power Very large area Kyser et al U.S. Pat. No. electric such as lead consumption required for actuator 3,946,398 lanthanum zirconate Many ink types Difficult to Zoltan U.S. Pat. No. (PZT) is electrically can be used integrate with 3,683,212 activated, and either Fast operation electronics 1973 Stemme expands, shears, or High efficiency High voltage U.S. Pat. No. 3,747,120 bends to apply drive transistors Epson Stylus pressure to the ink, required Tektronix ejecting drops. Full pagewidth IJ04 print heads impractical due to actuator size Requires electrical poling in high field strengths during manufacture Electro- An electric field is Low power Low maximum Seiko Epson, strictive used to activate consumption strain (approx. Usui et all JP electrostriction in Many ink types 0.01%) 253401/96 relaxor materials such can be used Large area IJ04 as lead lanthanum Low thermal required for actuator zirconate titanate expansion due to low strain (PLZT) or lead Electric field Response speed magnesium niobate strength required is marginal (˜10 (PMN). (approx. 3.5 V/&mgr;m) &mgr;s) can be generated High voltage without difficulty drive transistors Does not require required electrical poling Full pagewidth print heads impractical due to actuator size Ferro- An electric field is Low power Difficult to IJ04 electric used to induce a phase consumption integrate with transition between the Many ink types electronics antiferroelectric (AFE) can be used Unusual and ferroelectric (FE) Fast operation materials such as phase. Perovskite (<1 &mgr;s) PLZSnT are materials such as tin Relatively high required modified lead longitudinal strain Actuators require lanthanum zirconate High efficiency a large area titanate (PLZSnT) Electric field exhibit large strains of strength of around 3 up to 1% associated V/&mgr;m can be readily with the AFE to FE provided phase transition. Electro- Conductive plates are Low power Difficult to IJ02, IJ04 static plates separated by a consumption operate electrostatic compressible or fluid Many ink types devices in an dielectric (usually air). can be used aqueous Upon application of a Fast operation environment voltage, the plates The electrostatic attract each other and actuator will displace ink, causing normally need to be drop ejection. The separated from the conductive plates may ink be in a comb or Very large area honeycomb structure, required to achieve or stacked to increase high forces the surface area and High voltage therefore the force. drive transistors may be required Full pagewidth print heads are not competitive due to actuator size Electro- A strong electric field Low current High voltage 1989 Saito et al, static pull is applied to the ink, consumption required U.S. Pat. No. 4,799,068 on ink whereupon Low temperature May be damaged 1989 Miura et al, electrostatic attraction by sparks due to air U.S. Pat. No. 4,810,954 accelerates the ink breakdown Tone-jet towards the print Required field medium. strength increases as the drop size decreases High voltage drive transistors required Electrostatic field attracts dust Permanent An electromagnet Low power Complex IJ07, IJ10 magnet directly attracts a consumption fabrication electro- permanent magnet, Many ink types Permanent magnetic displacing ink and can be used magnetic material causing drop ejection. Fast operation such as Neodymium Rare earth magnets High efficiency Iron Boron (NdFeB) with a field strength Easy extension required. around 1 Tesla can be from single nozzles High local used. Examples are: to pagewidth print currents required Samarium Cobalt heads Copper (SaCo) and magnetic metalization should materials in the be used for long neodymium iron boron electromigration family (NdFeB, lifetime and low NdDyFeBNb, resistivity NdDyFeB, etc) Pigmented inks are usually infeasible Operating temperature limited to the Curie temperature (around 540 K) Soft A solenoid induced a Low power Complex IJ01, IJ05, IJ08, magnetic magnetic field in a soft consumption fabrication IJ10, IJ12, IJ14, core electro- magnetic core or yoke Many ink types Materials not IJ15, IJ17 magnetic fabricated from a can be used usually present in a ferrous material such Fast operation CMOS fab such as as electroplated iron High efficiency NiFe, CoNiFe, or alloys such as CoNiFe Easy extension CoFe are required [1], CoFe, or NiFe from single nozzles High local alloys. Typically, the to pagewidth print currents required soft magnetic material heads Copper is in two parts, which metalization should are normally held be used for long apart by a spring. electromigration When the solenoid is lifetime and low actuated, the two parts resistivity attract, displacing the Electroplating is ink. required High saturation flux density is required (2.0-2.1 T is achievable with CoNiFe [1]) Lorenz The Lorenz force Low power Force acts as a IJ06, IJ11, IJ13, force acting on a current consumption twisting motion IJ16 carrying wire in a Many ink types Typically, only a magnetic field is can be used quarter of the utilized. Fast operation solenoid length This allows the High efficiency provides force in a magnetic field to be Easy extension useful direction supplied externally to from single nozzles High local the print head, for to pagewidth print currents required example with rare heads Copper earth permanent metalization should magnets. be used for long Only the current electromigration carrying wire need be lifetime and low fabricated on the print- resistivity head, simplifying Pigmented inks materials are usually requirements. infeasible Magneto- The actuator uses the Many ink types Force acts as a Fischenbeck, striction giant magnetostrictive can be used twisting motion U.S. Pat. No. 4,032,929 effect of materials Fast operation Unusual IJ25 such as Terfenol-D (an Easy extension materials such as alloy of terbium, from single nozzles Terfenol-D are dysprosium and iron to pagewidth print required developed at the Naval heads High local Ordnance Laboratory, High force is currents required hence Ter-Fe-NOL). available Copper For best efficiency, the metalization should actuator should be pre- be used for long stressed to approx. 8 electromigration MPa. lifetime and low resistivity Pre-stressing may be required Surface Ink under positive Low power Requires Silverbrook, EP tension pressure is held in a consumption supplementary force 0771 658 A2 and reduction nozzle by surface Simple to effect drop related patent tension. The surface construction separation applications tension of the ink is No unusual Requires special reduced below the materials required in ink surfactants bubble threshold, fabrication Speed may be causing the ink to High efficiency limited by surfactant egress from the Easy extension properties nozzle. from single nozzles to pagewidth print heads Viscosity The ink viscosity is Simple Requires Silverbrook, EP reduction locally reduced to construction supplementary force 0771 658 A2 and select which drops are No unusual to effect drop related patent to be ejected. A materials required in separation applications viscosity reduction can fabrication Requires special be achieved Easy extension ink viscosity electrothermally with from single nozzles properties most inks, but special to pagewidth print High speed is inks can be engineered heads difficult to achieve for a 100:1 viscosity Requires reduction. oscillating ink pressure A high temperature difference (typically 80 degrees) is required Acoustic An acoustic wave is Can operate Complex drive 1993 Hadimioglu generated and without a nozzle circuitry et al, EUP 550,192 focussed upon the plate Complex 1993 Elrod et al, drop ejection region. fabrication EUP 572,220 Low efficiency Poor control of drop position Poor control of drop volume Thermo- An actuator which Low power Efficient aqueous IJ03, IJ09, IJ17, elastic bend relies upon differential consumption operation requires a IJ18, IJ19, IJ20, actuator thermal expansion Many ink types thermal insulator on IJ21, IJ22, IJ23, upon Joule heating is can be used the hot side IJ24, IJ27, IJ28, used. Simple planar Corrosion IJ29, IJ30, IJ31, fabrication prevention can be IJ32, IJ33, IJ34, Small chip area difficult IJ35, IJ36, IJ37, required for each Pigmented inks IJ38, IJ39, IJ40, actuator may be infeasible, IJ41 Fast operation as pigment particles High efficiency may jam the bend CMOS actuator compatible voltages and currents Standard MEMS processes can be used Easy extension from single nozzles to pagewidth print heads High CTE A material with a very High force can Requires special IJ09, IJ17, IJ18, thermo- high coefficient of be generated material (e.g. PTFE) IJ20, IJ21, IJ22, elastic thermal expansion Three methods of Requires a PTFE IJ23, IJ24, IJ27, actuator (CTE) such as PTFE deposition are deposition process, IJ28, IJ29, IJ30, polytetrafluoroethylene under development: which is not yet IJ31, IJ42, IJ43, (PTFE) is used. As chemical vapor standard in ULSI IJ44 high CTE materials deposition (CVD), fabs are usually non- spin coating, and PTFE deposition conductive, a heater evaporation cannot be followed fabricated from a PTFE is a with high conductive material is candidate for low temperature (above incorporated. A 50 &mgr;m dielectric constant 350° C.) processing long PTFE bend insulation in ULSI Pigmented inks actuator with Very low power may be infeasible, polysilicon heater and consumption as pigment particles 15 mW power input Many ink types may jam the bend can provide 180 &mgr;N can be used actuator force and 10 &mgr;m Simple planar deflection. Actuator fabrication motions include: Small chip area Bend required for each Push actuator Buckle Fast operation Rotate High efficiency CMOS compatible voltages and currents Easy extension from single nozzles to pagewidth print heads Conductive A polymer with a high High force can Requires special IJ24 polymer coefficient of thermal be generated materials thermo- expansion (such as Very low power development (High elastic PTFE) is doped with consumption CTE conductive actuator conducting substances Many ink types polymer) to increase its can be used Requires a PTFE conductivity to about 3 Simple planar deposition process, orders of magnitude fabrication which is not yet below that of copper. Small chip area standard in ULSI The conducting required for each fabs polymer expands actuator PTFE deposition when resistively Fast operation cannot be followed heated. High efficiency with high Examples of CMOS temperature (above conducting dopants compatible voltages 350° C.) processing include: and currents Evaporation and Carbon nanotubes Easy extension CVD deposition Metal fibers from single nozzles techniques cannot Conductive polymers to pagewidth print be used such as doped heads Pigmented inks polythiophene may be infeasible, Carbon granules as pigment particles may jam the bend actuator Shape A shape memory alloy High force is Fatigue limits IJ26 memory such as TiNi (also available (stresses maximum number alloy known as Nitinol - of hundreds of MPa) of cycles Nickel Titanium alloy Large strain is Low strain (1%) developed at the Naval available (more than is required to extend Ordnance Laboratory) 3%) fatigue resistance is thermally switched High corrosion Cycle rate between its weak resistance limited by heat martensitic state and Simple removal its high stiffness construction Requires unusual austenic state. The Easy extension materials (TiNi) shape of the actuator from single nozzles The latent heat of in its martensitic state to pagewidth print transformation must is deformed relative to heads be provided the austenic shape. Low voltage High current The shape change operation operation causes ejection of a Requires pre- drop. stressing to distort the martensitic state BASIC OPERATION MODE Description Advantages Disadvantages Examples Actuator This is the simplest mode of Simple operation Drop repetition rate is usually Thermal ink jet directly pushes operation: the actuator directly No external fields required limited to around 10 kHz. How- Piezoelectric ink jet ink supplies sufficient kinetic energy Satellite drops can be avoided if ever, this is not fundamental to IJ01, IJ02, IJ03, IJ04, IJ05, IJ06, to expel the drop. The drop must drop velocity is less than 4 m/s the method, but is related to the IJ07, IJ09, IJ11, IJ12, IJ14, IJ16, have a sufficient velocity to Can be efficient, depending refill method normally used IJ20, IJ22, IJ23, IJ24, IJ25, IJ26, overcome the surface tension. upon the actuator used All of the drop kinetic energy IJ27, IJ28, IJ29, IJ30, IJ31, IJ32, must be provided by the actuator IJ33, IJ34, IJ35, IJ36, IJ37, IJ38, Satellite drops usually form if IJ39, IJ40, IJ41, IJ42, IJ43, IJ44 drop velocity is greater than 4.5 m/s Proximity The drops to be printed are Very simple print head fabrica- Requires close proximity Silverbrook, EP 0771 658 A2 selected by some manner (e.g. tion can be used between the print head and the and related patent applications thermally induced surface The drop selection means does print media or transfer roller tension reduction of pressurized not need to provide the energy May require two print heads ink). Selected drops are required to separate the drop printing alternate rows of the separated from the ink in the from the nozzle image nozzle by contract with the Monolithic color print heads are print medium or a transfer difficult roller. Electrostatic The drops to be printed are Very simple print head fabrica- Requires very high electrostatic Silverbrook, EP 0771 658 A2 pull on ink selected by some manner (e.g. tion can be used field and related patent applications thermally induced surface The drop selection means does Electrostatic field for small Tone-Jet tension reduction of pressurized not need to provide the energy nozzle sizes is above air break- ink). Selected drops are required to separate the drop down separated from the ink in the from the nozzle Electrostatic field may attract nozzle by a strong electric field. dust Magnetic pull The drops to be printed are Very simple print head fabrica- Requires magnetic ink Silverbrook, EP 0771 658 A2 on ink selected by some manner (e.g. tion can be used Ink colors other than black are and related patent applications thermally induced surface The drop selection means does difficult tension reduction of pressurized not need to provide the energy Requires very high magnetic ink). Selected drops are required to separate the drop fields separated from the ink in the from the nozzle nozzle by a strong magnetic field acting on the magnetic ink. Shutter The actuator moves a shutter to High speed (>50 kHz) operation Moving parts are required IJ13, IJ17, IJ21 block ink flow to the nozzle. can be achieved due to reduced Requires ink pressure modulator The ink pressure is pulsed at a refill time Friction and wear must be multiple of the drop ejection Drop timing can be very considered frequency. accurate Stiction is possible The actuator energy can be very low Shuttered grill The actuator moves a shutter to Actuators with small travel can Moving parts are required IJ08, IJ15, IJ18, IJ19 block ink flow through a grill to be used Requires ink pressure modulator the nozzle. The shutter move- Actuators with small force can Friction and wear must be ment need only be equal to the be used considered width of the grill holes. High speed (>50 kHz) operation Stiction is possible can be achieved Pulsed mag- A pulsed magnetic field attracts Extremely low energy operation Requires an external pulsed IJ10 netic pull on an ‘ink pusher’ at the drop is possible magnetic field ink pusher ejection frequency. An actuator No heat dissipation problems Requires special materials for controls a catch, which prevents both the actuator and the ink the ink pusher from moving pusher when a drop is not to be ejected. Complex construction AUXILIARY MECHANISM (APPLIED TO ALL NOZZLES) Description Advantages Disadvantages Examples None The actuator directly fires the Simplicity of construction Drop ejection energy must be Most ink jets, including piezo- ink drop, and there is no external Simplicity of operation supplied by individual nozzle electric and thermal bubble. field or other mechanism Small physical size actuator IJ01, IJ02, IJ03, IJ04, IJ05, IJ07, required. IJ09, IJ11, IJ12, IJ14, IJ20, IJ22, IJ23, IJ24, IJ25, IJ26, IJ27, IJ28, IJ29, IJ30, IJ31, IJ32, IJ33, IJ34, IJ35, IJ36, IJ37, IJ38, IJ39, IJ40, IJ41, IJ42, IJ43, IJ44 Oscillating ink The ink pressure oscillates, Oscillating ink pressure can Requires external ink pressure Silverbrook, EP 0771 658 A2 pressure providing much of the drop provide a refill pulse, allowing oscillator and related patent applications (including ejection energy. The actuator higher operating speed Ink pressure phase and IJ08, IJ13, IJ15, IJ17, IJ18, IJ19, acoustic selects which drops are to be The actuators may operate with amplitude must be carefully IJ21 stimulation) fired by selectively blocking much lower energy controlled or enabling nozzles. The ink Acoustic lenses can be used to Acoustic reflections in the ink pressure oscillation may be focus the sound on the nozzles chamber must be designed for achieved by vibrating the print head, or preferably by an actuator in the ink supply. Media The print head is placed in close Low power Precision assembly required Silverbrook, EP 0771 658 A2 proximity proximity to the print medium. High accuracy Paper fibers may cause problems and related patent applications Selected drops protrude from the Simple print head construction Cannot print on rough substrates print head further than un- selected drops, and contact the print medium. The drop soaks into the medium fast enough to cause drop separation. Transfer roller Drops are printed to a transfer High accuracy Bulky Silverbrook, EP 0771 658 A2 roller instead of straight to the Wide range of print substrates Expensive and related patent applications print medium. A transfer roller can be used Complex construction Tektronix hot melt piezoelectric can also be used for proximity Ink can be dried on the transfer ink jet drop separation. roller Any of the IJ series Electrostatic An electric field is used to Low power Field strength required for Silverbrook, EP 0771 658 A2 accelerate selected drops Simple print head construction separation of small drops is and related patent applications towards the print medium. near or above air breakdown Tone-Jet Direct mag- A magnetic field is used to Low power Requires magnetic ink Silverbrook, EP 0771 658 A2 netic field accelerate selected drops of Simple print head construction Requires strong magnetic field and related patent applications magnetic ink towards the print medium. Cross magnetic The print head is placed in a Does not require magnetic Requires external magnet IJ06, IJ16 field constant magnetic field. The materials to be integrated in the Current densities may be high, Lorenz force in a current print head manufacturing resulting in electromigration carrying wire is used to move process problems the actuator. Pulsed mag- A pulsed magnetic field is used Very low power operation is Complex print head construction IJ10 netic field to cyclically attract a paddle, possible Magnetic materials required in which pushes on the ink. A Small print head size print head small actuator moves a catch, which selectively prevents the paddle from moving. ACTUATOR AMPLIFICATION OR MODIFICATION METHOD Description Advantages Disadvantages Examples None No actuator mechanical ampli- Operational simplicity Many actuator mechanisms have Thermal Bubble Ink jet fication is used. The actuator insufficient travel, or insufficient IJ01, IJ02, IJ06, IJ07, IJ16, IJ25, directly drives the drop ejection force, to efficiently drive the IJ26 process. drop ejection process Differential An actuator material expands Provides greater travel in a High stresses are involved Piezoelectric expansion bend more on one side than on the reduced print head area Care must be taken that the IJ03, IJ09, IJ17, IJ18, IJ19, IJ20, actuator other. The expansion may be materials do not delaminate IJ21, IJ22, IJ23, IJ24, IJ27, IJ29, thermal, piezoelectric, magneto- Residual bend resulting from IJ30, IJ31, IJ32, IJ33, IJ34, IJ35, strictive, or other mechanism. high temperature or high stress IJ36, IJ37, IJ38, IJ39, IJ42, IJ43, The bend actuator converts a during formation IJ44 high force low travel actuator mechanism to high travel, lower force mechanism. Transient bend A trilayer bend actuator where Very good temperature stability High stresses are involved IJ40, IJ41 actuator the two outside layers are High speed, as a new drop can Care must be taken that the identical. This cancels bend due be fired before heat dissipates materials do not delaminate to ambient temperature and Cancels residual stress of residual stress. The actuator only formation responds to transient heating of one side or the other. Reverse spring The actuator loads a spring. Better coupling to the ink Fabrication complexity IJ05, IJ11 When the actuator is turned off, High stress in the spring the spring releases. This can reverse the force/distance curve of the actuator to make it compatible with the force/time requirements of the drop ejection. Actuator stack A series of thin actuators are Increased travel Increased fabrication complexity Some piezoelectric ink jets stacked. This can be appropriate Reduced drive voltage Increased possibility of short IJ04 where actuators require high circuits due to pinholes electric field strength, such as electrostatic and piezoelectric actuators. Multiple Multiple smaller actuators are Increases the force available Actuator forces may not add IJ12, IJ13, IJ18, IJ20, IJ22, IJ28, actuators used simultaneously to move the from an actuator linearly, reducing efficiency IJ42, IJ43 ink. Each actuator need provide Multiple actuators can be only a portion of the force positioned to control ink flow required. accurately Linear Spring A linear spring is used to trans- Matches low travel actuator with Requires print head area for the IJ15 form a motion with small travel higher travel requirements spring and high force into a longer Non-contact method of motion travel, lower force motion. transformation Coiled actuator A bend actuator is coiled to Increase travel Generally restricted to planar IJ17, IJ21, IJ34, IJ35 provide greater travel in a Reduces chip area implementations due to extreme reduced chip area. Planar implementations are fabrication difficulty in other relatively easy to fabricate. orientations. Flexure bend A bend actuator has a small Simple means of increasing Care must be taken not to IJ10, IJ19, IJ33 actuator region near the fixture point, travel of a bend actuator exceed the elastic limit in the which flexes much more readily flexure area than the remainder of the Stress distribution is very actuator. The actuator flexing uneven is effectively converted from an Difficult to accurately model even coiling to an angular bend, with finite element analysis resulting in greater travel of the actuator tip. Catch The actuator controls a small Very low actuator energy Complex construction IJ10 catch. The catch either enables Very small actuator size Requires external force or disables movement of an ink Unsuitable for pigmented inks pusher that is controlled in a bulk manner. Gears Gears can be used to increase Low force, low travel actuators Moving parts are required IJ13 travel at the expense of duration. can be used Several actuator cycles are Circular gears, rack and pinion, Can be fabricated using standard required ratchets, and other gearing surface MEMS processes More complex drive electronics methods can be used. Complex construction Friction, friction, and wear are possible Buckle plate A buckle plate can be used to Very fast movement achievable Must stay within elastic limits of S. Hirata et al, “An Ink-jet Head change a slow actuator into a the materials for long device life Using Diaphragm Micro- fast motion. It can also convert High stresses involved actuator”, Proc. IEEE MEMS, a high force, low travel actuator Generally high power require- Feb. 1996, pp 418-423. into a high travel, medium force ment IJ18, IJ27 motion. Tapered mag- A tapered magnetic pole can Linearizes the magnetic force/ Complex construction IJ14 netic pole increase travel at the expense distance curve of force. Lever A lever and fulcrum is used to Matches low travel actuator with High stress around the fulcrum IJ32, IJ36, IJ37 transform a motion with small higher travel requirements travel and high force into a Fulcrum area has no linear motion with longer travel and movement, and can be used for a lower force. The lever can also fluid seal reverse the direction of travel. Rotary impeller The actuator is connected to a High mechanical advantage Complex construction IJ28 rotary impeller. A small angular The ratio of force to travel of Unsuitable for pigmented inks deflection of the actuator results the actuator can be matched to in a rotation of the impeller the nozzle requirements by vanes, which push the ink varying the number of impeller against stationary vanes and out vanes of the nozzle. Acoustic lens A refractive or diffractive (e.g. No moving parts Large area required 1993 Hadimioglu et al, EUP zone plate) acoustic lens is used Only relevant for acoustic ink 550,192 to concentrate sound waves. jets 1993 Elrod et al, EUP 572,220 Sharp con- A sharp point is used to concen- Simple construction Difficult to fabricate using Tone-jet ductive point trate an electrostatic field. standard VLSI processes for a surface ejecting ink-jet Only relevent for electrostatic ink jets ACTUATOR MOTION Description Advantages Disadvantages Examples Volume The volume of the actuator Simple construction in the case High energy is typically required Hewlett-Packard Thermal Ink jet expansion changes, pushing the ink in all of thermal ink jet to achieve volume expansion. Canon Bubblejet directions. This leads to thermal stress, cavitation, and kogation in thermal ink jet implementations Linear, normal The actuator moves in a Efficient coupling to ink drops High fabrication complexity may IJ01, IJ02, IJ04, IJ07, IJ11, IJ14 to chip surface direction normal to the print ejected normal to the surface be required to achieve per- head surface. The nozzle is pendicular motion typically in the line of movement. Parallel to The actuator moves parallel to Suitable for planar fabrication Fabrication complexity IJ12, IJ13, IJ15, IJ33, IJ34, IJ35, chip surface the print head surface. Drop Friction IJ36 ejection may still be normal to Stiction the surface. Membrane An actuator with a high force The effective area of the actuator Fabrication complexity 1982 Howkins U.S. Pat. No. push but small area is used to push a becomes the membrane area Actuator size 4,459,601 stiff membrane that is in contact Difficulty of integration in a with the ink. VLSI process Rotary The actuator causes the rotation Rotary levers may be used to Device complexity IJ05, IJ08, IJ13, IJ28 of some element, such a grill or increase travel May have friction at a pivot impeller Small chip area requirements point Bend The actuator bends when A very small change in Requires the actuator to be made 1970 Kyser et al U.S. Pat. No. energized. This may be due to dimensions can be converted to from at least two distinct layers, 3,946,398 differential thermal expansion, a large motion. or to have a thermal difference 1973 Stemme U.S. Pat. No. piezoelectric expansion, mag- across the actuator 3,747,120 netostriction, or other form of IJ03, IJ09, IJ10, IJ19, IJ23, IJ24, relative dimensional change. IJ25, IJ29, IJ30, IJ31, IJ33, IJ34, IJ35 Swivel The actuator swivels around a Allows operation where the net Inefficient coupling to the ink IJ06 central pivot. This motion is linear force on the paddle is zero motion suitable where there are opposite Small chip area requirements forces applied to opposite sides of the paddle, e.g. Lorenz force. Straighten The actuator is normally bent, Can be used with shape memory Requires careful balance of IJ26, IJ32 and straightens when energized. alloys where the austenic phase stresses to ensure that the is planar quiescent bend is accurate Double bend The actuator bends in one One actuator can be used to Difficult to make the drops IJ36, IJ37, IJ38 direction when one element is power two nozzles. ejected by both bend directions energized, and bends the other Reduced chip size. identical. way when another element is Not sensitive to ambient A small efficiency loss energized. temperature compared to equivalent single bend actuators. Shear Energizing the actuator causes a Can increase the effective travel Not readily applicable to other 1985 Fishbeck U.S. Pat. No. shear motion in the actuator of piezoelectric actuators actuator mechanisms 4,584,590 material. Radial con- The actuator squeezes an ink Relatively easy to fabricate High force required 1970 Zoltan U.S. Pat. No. striction reservoir, forcing ink from a single nozzles from glass tubing Inefficient 3,683,212 constricted nozzle. as macroscopic structures Difficult to integrate with VLSI processes Coil/uncoil A coiled actuator uncoils or coils Easy to fabricate as a planar Difficult to fabricate for non- IJ17, IJ21, IJ34, IJ35 more tightly. The motion of the VLSI process planar devices free end of the actuator ejects Small area required, therefore Poor out-of-plane stiffness the ink. low cost Bow The actuator bows (or buckles) Can increase the speed of travel Maximum travel is constrained IJ16, IJ18, IJ27 in the middle when energized. Mechanically rigid High force required Push-Pull Two actuators control a shutter. The structure is pinned at both Not readily suitable for ink jets IJ18 One actuator pulls the shutter, ends, so has a high out-of-plane which directly push the ink and the other pushes it. rigidity Curl inwards A set of actuators curl inwards Good fluid flow to the region Design complexity IJ20, IJ42 to reduce the volume of ink that behind the actuator increases they enclose. efficiency Curl outwards A set of actuators curl outwards, Relatively simple construction Relatively large chip area IJ43 pressurizing ink in a chamber surrounding the actuators, and expelling ink from a nozzle in the chamber. Iris Multiple vanes enclose a volume High efficiency High fabrication complexity IJ22 of ink. These simultaneously Small chip area Not suitable for pigmented inks rotate, reducing the volume between the vanes. Acoustic The actuator vibrates at a high The actuator can be physically Large area required for efficient 1993 Hadimioglu et al, EUP vibration frequency. distant from the ink operation at useful frequencies 550,192 Acoustic coupling and crosstalk 1993 Elrod et al, EUP 572,220 Complex drive circuitry Poor control drop volume and position None In various ink jet designs the No moving parts Various other tradeoffs are Silverbrook, EP 0771 658 A2 actuator does not move. required to eliminate moving and related patent applications parts Tone-jet NOZZLE REFILL METHOD Description Advantages Disadvantages Examples Surface tension This is the normal way that ink Fabrication simplicity Low speed Thermal ink jet jets are refilled. After the Operational simplicity Surface tension force relatively Piezoelectric ink jet actuator is energized, it small compared to actuator force IJ01-IJ07, IJ10-IJ14, IJ16, IJ20, typically returns rapidly to its Long refill time usually IJ22-IJ45 normal position. This rapid dominates the total repetition return sucks in air through the rate nozzle opening. The ink surface tension at the nozzle then exerts a small force restoring the meniscus to a minimum area. This force refills the nozzle. Shuttered Ink to the nozzle chamber is High speed Requires common ink pressure IJ08, IJ13, IJ15, IJ17, IJ18, IJ19, oscillating provided at a pressure that Low actuator energy, as the oscillator IJ21 ink pressure oscillates at twice the drop actuator need only open or close May not be suitable for pig- ejection frequency. When a drop the shutter, instead of ejecting mented inks is to be ejected, the shutter is the ink drop opened for 3 half cycles: drop ejection, actuator return, and refill. The shutter is then closed to prevent the nozzle chamber emptying during the next negative pressure cycle. Refill actuator After the main actuator has High speed, as the nozzle is Requires two independent IJ09 ejected a drop a second (refill) actively refilled actuators per nozzle actuator is energized. The refill actuator pushes ink into the nozzle chamber. The refill actuator returns slowly, to pre- vent its return from emptying the chamber again. Positive ink The ink is held a slight positive High refill rate, therefore a high Surface spill must be prevented Silverbrook, EP 0771 658 A2 pressure pressure. After the ink drop is drop repetition rate is possible Highly hydrophobic print head and related patent applications ejected, the nozzle chamber fills surfaces are required Alternative for: IJ01-IJ07, quickly as surface tension and IJ10-IJ14, IJ16, IJ20, IJ22-IJ45 ink pressure both operate to refill the nozzle. METHOD OF RESTRICTING BACK-FLOW THROUGH INLET Description Advantages Disadvantages Examples Long inlet The ink inlet channel to the Design simplicity Restricts refill rate Thermal ink jet channel nozzle chamber is made long Operational simplicity May result in a relatively large Piezoelectric ink jet and relatively narrow, relying on Reduces crosstalk chip area IJ42, IJ43 viscous drag to reduce inlet Only partially effective back-flow. Positive ink The ink is under a positive Drop selection and separation Requires a method (such as a Silverbrook, EP 0771 658 A2 pressure pressure, so that in the forces can be reduced nozzle rim or effective hydro- and related patent applications quiescent state some of the ink Fast refill time phobizing, or both) to prevent Possible operation of the drop already protrudes from the flooding of the ejection following: IJ01-IJ07, IJ09-IJ12, nozzle. This reduces the pressure surface of the print head. IJ14, IJ16, IJ20, IJ22, IJ23- in the nozzle chamber which is IJ34, IJ36-IJ41, IJ44 required to eject a certain volume of ink. The reduction in chamber pressure results in a reduction in ink pushed out through the inlet. Baffle One or more baffles are placed The refill rate is not as restricted Design complexity HP Thermal Ink Jet in the inlet ink flow. When the as the long inlet method. May increase fabrication Tektronix piezoelectric ink jet actuator is energized, the rapid Reduces crosstalk complexity (e.g. Tektronix hot ink movement creates eddies melt Piezoelectric print heads). which restrict the flow through the inlet. The slower refill process is unrestricted, and does not result in eddies. Flexible flap In this method recently disclosed Significantly reduces back-flow Not applicable to most ink jet Canon restricts inlet by Canon, the expanding for edge-shooter thermal ink jet configurations actuator (bubble) pushes on a devices Increased fabrication complexity flexible flap that resticts the Inelastic deformation of polymer inlet. flap results in creep over extended use Inlet filter A filter is located between the Additional advantage of ink fil- Restricts refill rate IJ04, IJ12, IJ24, IJ27, IJ29, IJ30 ink inlet and the nozzle tration May result in complex con- chamber. The filter has a multi- Ink filter may be fabricated with struction tude of small holes or slots, no additional process steps restricting ink flow. The filter also removes particles which may block the nozzle. Small inlet The ink inlet channel to the Design simplicity Restricts refill rate IJ02, IJ37, IJ44 compared to nozzle chamber has a sub- May result in a relatively large nozzle stantially smaller cross section chip area than that of the nozzle, resulting Only partially effective in easier ink egress out of the nozzle than out of the inlet. Inlet shutter A secondary actuator controls Increases speed of the ink-jet Requires separate refill actuator IJ09 the position of a shutter, closing print head operation and drive circuit off the ink inlet when the main actuator is energized. The inlet is The method avoids the problem Back-flow problem is eliminated Requires careful design to IJ01, IJ03, IJ05, IJ06, IJ07, IJ10, located behind of inlet back-flow by arranging minimize the negative pressure IJ11, IJ14, IJ16, IJ22, IJ23, IJ25, the ink-pushing the ink-pushing surface of the behind the paddle IJ28, IJ31, IJ32, IJ33, IJ34, IJ35, surface actuator between the inlet and IJ36, IJ39, IJ40, IJ41 the nozzle. Part of the The actuator and a wall of the Significant reductions in back- Small increases in fabrication IJ07, IJ20, IJ26, IJ38 actuator moves ink chamber are arranged so that flow can be achieved complexity to shut off the the motion of the actuator Compact designs possible inlet closes off the inlet. Nozzle actuator In some configurations of ink Ink back-flow problem is None related to ink back-flow on Silverbrook, EP 0771 658 A2 does not result jet, there is no expansion or eliminated actuation and related patent applications in ink back- movement of an actuator which Valve-jet flow may cause ink back-flow Tone-jet through the inlet. NOZZLE CLEARING METHOD Description Advantages Disadvantages Examples Normal nozzle All of the nozzles are fired No added complexity on the May not be sufficient to Most ink jet systems firing periodically, before the ink has print head displace dried ink IJ01, IJ02, IJ03, IJ04, IJ05, IJ06, a chance to dry. When not in use IJ07, IJ09, IJ10, IJ11, IJ12, IJ14, the nozzles are sealed (capped) IJ16, IJ20, IJ22, IJ23, IJ24, IJ25, against air. The nozzle firing is IJ26, IJ27, IJ28, IJ29, IJ30, IJ31, usually performed during a IJ32, IJ33, IJ34, IJ36, IJ37, IJ38, special clearing cycle, after first IJ39, IJ40, IJ41, IJ42, IJ43, IJ44, moving the print head to a IJ45 cleaning station. Extra power In systems which heat the ink, Can be highly effective if the Requires higher drive voltage for Silverbrook, EP 0771 658 A2 to ink heater but do not boil it under normal heater is adjacent to the nozzle clearing and related patent applications situations, nozzle clearing can May require larger drive be achieved by over-powering transistors the heater and boiling ink at the nozzle. Rapid success- The actuator is fired in rapid Does not require extra drive Effectiveness depends sub- May be used with: IJ01, IJ02, ion of actuator succession. In some configura- circuits on the print head stantially upon the configuration IJ03, IJ04, IJ05, IJ06, IJ07, IJ09, pulses tions, this may cause heat build- Can be readily controlled and of the ink jet nozzle IJ10, IJ11, IJ14, IJ16, IJ20, IJ22, up at the nozzle which boils the initiated by digital logic IJ23, IJ24, IJ25, IJ27, IJ28, IJ29, ink, clearing the nozzle. In other IJ30, IJ31, IJ32, IJ33, IJ34, IJ36, situations, it may cause IJ37, IJ38, IJ39, IJ40, IJ41, IJ42, sufficient vibrations to dislodge IJ43, IJ44, IJ45 clogged nozzles. Extra power to Where an actuator is not A simple solution where Not suitable where there is a May be used with: IJ03, IJ09, ink pushing normally driven to the limit of applicable hard limit to actuator movement IJ16, IJ20, IJ23, IJ24, IJ25, IJ27, actuator its motion, nozzle clearing may IJ29, IJ30, IJ31, IJ32, IJ39, IJ40, be assisted by providing an IJ41, IJ42, IJ43, IJ44, IJ45 enhanced drive signal to the actuator. Acoustic An ultrasonic wave is applied to A high nozzle clearing capability High implementation cost if IJ08, IJ13, IJ15, IJ17, IJ18, IJ19, resonance the ink chamber. This wave is of can be achieved system does not already include IJ21 an appropriate amplitude and May be implemented at very low an acoustic actuator frequency to cause sufficient cost in systems which already force at the nozzle to clear include acoustic actuators blockages. This is easiest to achieve if the ultrasonic wave is at a resonant frequency of the ink cavity. Nozzle clearing A microfabricated plate is Can clear severely clogged Accurate mechanical alignment Silverbrook, EP 0771 658 A2 plate pushed against the nozzles. The nozzles is required and related patent applications plate has a post for every nozzle. Moving parts are required A post moves through each There is risk of damage to the nozzle, displacing dried ink. nozzles Accurate fabrication is required Ink pressure The pressure of the ink is May be effective where other Requires pressure pump or other May be used with all IJ series pulse temporarily increased so that methods cannot be used pressure actuator ink jets ink streams from all of the Expensive nozzles. This may be used in Wasteful of ink conjunction with actuator energizing. Print head A flexible ‘blade’ is wiped Effective for planar print head Difficult to use if print head Many ink jet systems wiper across the print head surface. surfaces surface is non-planar or very The blade is usually fabricated Low cost fragile from a flexible polymer, e.g. Requires mechanical parts rubber or synthetic elastomer. Blade can wear out in high volume print systems Separate ink A separate heater is provided at Can be effective where other Fabrication complexity Can be used with many IJ series boiling heater the nozzle although the normal nozzle clearing methods cannot ink jets drop e-ection mechanism does be used not require it. The heaters do not Can be implemented at no require individual drive circuits, additional cost in some ink jet as many nozzles can be cleared configurations simultaneously, and no imaging is required. NOZZLE PLATE CONSTRUCTION Description Advantages Disadvantages Examples Electroformed A nozzle plate is separately Fabrication simplicity High temperatures and pressures Hewlett Packard Thermal Ink jet nickel fabricated from electroformed are required to bond nozzle plate nickel, and bonded to the print Minimum thickness constraints head chip. Differential thermal expansion Laser ablated Individual nozzle holes are No mask required Each hole must be individually Canon Bubblejet or drilled ablated by an intense UV laser Can be quite fast formed 1988 Sercel et al., SPIE, Vol. polymer in a nozzle plate, which is Some control over nozzle profile Special equipment required 998 Excimer Beam Applica- typically a polymer such as is possible Slow where there are many tions, pp. 76-83 polyimide or polysulphone Equipment required is relatively thousands of nozzles per print 1993 Watanabe et al., U.S. Pat. low cost head No. 5,208,604 May produce thin burrs at exit holes Silicon micro- A separate nozzle plate is micro- High accuracy is attainable Two part construction K. Bean, IEEE Transactions on machined machined from single crystal High cost Electron Devices, Vol. ED-25, silicon, and bonded to the print Requires precision alignment No. 10, 1978, pp 1185-1195 head wafer. Nozzles may be clogged by Xerox 1990 Hawkins et al., U.S. adhesive Pat. No. 4,899,181 Glass Fine glass capillaries are drawn No expensive equipment Very small nozzle sizes are 1970 Zoltan U.S. Pat. No. capillaries from glass tubing. This method required difficult to form 3,683,212 has been used for making Simple to make single nozzles Not suited for mass production individual nozzles, but is difficult to use for bulk manufacturing of print heads with thousands of nozzles. Monolithic, The nozzle plate is deposited as High accuracy (<1 &mgr;m) Requires sacrificial layer under Silverbrook, EP 0771 658 A2 surface micro- a layer using standard VLSI Monolithic the nozzle plate to form the and related patent applications machined using deposition techniques. Nozzles Low cost nozzle chamber IJ01, IJ02, IJ04, IJ11, IJ12, IJ17, VLSI litho- are etched in the nozzle plate Existing processes can be used Surface may be fragile to the IJ18, IJ20, IJ22, IJ24, IJ27, IJ28, graphic pro- using VLSI lithography and touch IJ29, IJ30, IJ31, IJ32, IJ33, IJ34, cesses etching. IJ36, IJ37, IJ38, IJ39, IJ40, IJ41, IJ42, IJ43, IJ44 Monolithic, The nozzle plate is a buried etch High accuracy (<1 &mgr;m) Requires long etch times IJ03, IJ05, IJ06, IJ07, IJ08, IJ09, etched through stop in the wafer. Nozzle Monolithic Requires a support wafer IJ10, IJ13, IJ14, IJ15, IJ16, IJ19, substrate chambers are etched in the front Low cost IJ21, IJ23, IJ25, IJ26 of the wafer, and the wafer is No differential expansion thinned from the back side. Nozzles are then etched in the etch stop layer. No nozzle plate Various methods have been tried No nozzles to become clogged Difficult to control drop position Ricoh 1995 Sekiya et al U.S. to eliminate the nozzles entirely, accurately Pat. No. 5,412,413 to prevent nozzle clogging. Crosstalk problems 1993 Hadimioglu et al EUP These include thermal bubble 550,192 mechanisms and acoustic lens 1993 Elrod et al EUP 572,220 mechanisms Trough Each drop ejector has a trough Reduced manufacturing Drop firing direction is sensitive IJ35 through which a paddle moves. complexity to wicking. There is no nozzle plate. Monolithic Nozzle slit The elimination of nozzle holes No nozzles to become clogged Difficult to control drop position 1989 Saito et al U.S. Pat. No. instead of and replacement by a slit accurately 4,799,068 individual encompassing many actuator Crosstalk problems nozzles positions reduces nozzle clogging, but increases crosstalk due to ink surface waves DROP EJECTION DIRECTION Description Advantages Disadvantages Examples Edge (‘edge Ink flow is along the surface of Simple construction Nozzles limited to edge Canon Bubblejet 1979 Endo et shooter’) the chip, and ink drops are No silicon etching required High resolution is difficult al GB patent 2,007,162 ejected from the chip edge. Good heat sinking via substrate Fast color printing requires one Xerox heater-in-pit 1990 Mechanically strong print head per color Hawkins et al U.S. Pat. No. Ease of chip handing 4,899,181 Tone-jet Surface (‘roof Ink flow is along the surface of No bulk silicon etching required Maximum ink flow is severely Hewlett-Packard TIJ 1982 shooter’) the chip, and ink drops are Silicon can make an effective restricted Vaught et al U.S. Pat. No. ejected from the chip surface, heat sink 4,490,728 normal to the plane of the chip. Mechanical strength IJ02, IJ11, IJ12, IJ20, IJ22 Through chip, Ink flow is through the chip, and High ink flow Requires bulk silicon etching Silverbrook, EP 0771 658 A2 forward (‘up ink drops are ejected from the Suitable for pagewidth print and related patent applications shooter’) front surface of the chip. heads IJ04, IJ17, IJ18, IJ24, IJ27-IJ45 High nozzle packing density therefore low manufacturing cost Through chip, Ink flow is through the chip, and High ink flow Requires wafer thinning IJ01, IJ03, IJ05, IJ06, IJ07, IJ08, reverse (‘down ink drops are ejected from the Suitable for pagewidth print Requires special handling during IJ09, IJ10, IJ13, IJ14, IJ15, IJ16, shooter’) rear surface of the chip. heads manufacture IJ19, IJ21, IJ23, IJ25, IJ26 High nozzle packing density therefore low manufacturing cost Through Ink flow is through the actuator, Suitable for piezoelectric print Pagewidth print heads require Epson Stylus actuator which is not fabricated as part of heads several thousand connections to Tektronix hot melt piezoelectric the same substrate as the drive drive circuits ink jets transistors. Cannot be manufactured in standard CMOS fabs Complex assembly required INK TYPE Description Advantages Disadvantages Examples Aqueous, dye Water based ink which typically Environmentally friendly Slow drying Most existing ink jets contains: water, dye, surfactant, No order Corrosive All IJ series ink jets humectant, and biocide. Modern Bleeds on paper Silverbrook, EP 0771 658 A2 ink dyes have high water- May strikethrough and related patent applications fastness, light fastness Cockles paper Aqueous, pig- Water based ink which typically Environmentally friendly Slow drying IJ02, IJ04, IJ21, IJ26, IJ27, IJ30 ment contains: water, pigment, No odor Corrosive Silverbrook, EP 0771 658 A2 surfactant, humectant, and Reduced bleed Pigment may clog nozzles and related patent applications biocide. Pigments have an Reduced wicking Pigment may clog actuator Piezoelectric ink-jets advantage in reduced bleed, Reduced strikethrough mechanisms Thermal ink jets (with signifi- wicking and strikethrough. Cockles paper cant restrictions) Methyl Ethyl MEK is a highly volatile solvent Very fast drying Ketone (MEK) used for industrial printing on Prints on various substrates such Odorous All IJ series ink jets difficult surfaces such as as metals and plastics Flammable aluminum cans. Alcohol Alcohol based inks can be used Fast drying Slight odor All IJ series ink jets (ethanol, where the printer must operate at Operates at sub-freezing Flammable 2-butanol, and temperatures below the freezing temperatures others) point of water. An example of Reduced paper cockle this is in-camera consumer Low cost photographic printing. Phase change The ink is solid at room temper- No drying time-ink instantly High viscosity Tektronix hot melt piezoelectric (hot melt) ature, and is melted in the print freezes on the print medium Printed ink typically has a ink jets head before jetting. Hot melt Almost any print medium can be ‘waxy’ feel 1989 Nowak U.S. Pat. No. inks are usually wax based, with used Printed pages may ‘block’ 4,820,436 a melting point around 80° C.. No paper cockle occurs Ink temperature may be above All IJ series ink jets After jetting the ink freezes No wicking occurs the curie pont of permanent almost instantly upon contacting No bleed occurs magnets the print medium or a transfer No strikthrough occurs Ink heaters consume power roller. Long warm-up time Oil Oil based inks are extensively High solubility medium for High viscosity: this is a signifi- All IJ series ink jets used in offset printing. They some dyes cant limitation for use in ink have advantages in improved Does not cockle paper jets, which usually require a low characteristics on paper Does not wick through paper viscosity. Some short chain and (especially no wicking or multi-branched oils have a cockle). Oil soluble dies and sufficiently low viscosity. pigments are required. Slow drying Micro- A microemulsion is a stable, self Stop ink bleed Viscosity higher than water All IJ series ink jets emulsion forming emulsion of oil, water, High dye solubility Cost is slightly higher than and surfactant. The characteristic Water, oil, and amphiphilic water based ink drop size is less than 100 nm, soluble dies can be used High surfactant concentration and is determined by the pre- Can stabilize pigment required (around 5%) ferred curvature of the sur- suspensions factant.

Claims

1. An ink jet nozzle comprising:

a nozzle chamber having an ink ejection port in one wall of said chamber;

an ink supply source interconnected to said nozzle chamber;

a thermal actuator activated to eject ink from said nozzle chamber via said ink ejection port, said thermal actuator comprising two layers of actuator material having a high coefficient of thermal expansion, a top layer being substantially non conductive and a bottom layer comprising portions being conductive and portions being non-conductive such that a resistive circuit is formed for heating of the bottom layer through interaction of said conductive and non-conductive portions;

said thermal actuator being activated by means of passing a current through the bottom layer so as to cause it to expand relative to the top layer, which is cooled by the ink; and

said resistive circuit having predetermined area of low circuit cross-sectional area so as to produce high levels of heating of said actuators in those areas.

2. An ink jet nozzle as claimed in claim 1 wherein said top layer and said non-conductive portions of said bottom layer are formed from a same material.

3. An ink jet nozzle as claimed in claim 1 wherein the bottom layer of said actuator has a hydrophobic surface and wherein during operation said hydrophobic surface causes an air bubble to form under said thermal actuator.

4. An ink jet nozzle as claimed in claim 1 wherein the bottom layer of said actuator is air vented so as to reduce the actuation energy required to eject ink from said nozzle chamber.

5. An ink jet nozzle as claimed in claim 4 wherein said air venting comprises a series of small holes underneath the actuator, said holes being interconnected to an air supply channel for the supply of air to the back of said actuator.

6. An ink jet nozzle as claimed in claim 5 wherein said holes are of a size such that, during operation, any fluid is retained within said nozzle chamber.

7. An ink jet nozzle as claimed in claim 5 wherein said actuator is attached at on end to said nozzle chamber and said holes are located near said attached end.

8. An ink jet nozzle as claimed in claim 1 wherein an area around the bottom layer of said actuator is constructed from hydrophobic material.